Is it against the rules of the forum to use multiple accounts for signature campaigns or is it against the rules of signature campaign provider? That's an important distinction. A signature campaign provider is a private business and the forum should not ban someone because they violated the rules that the signature campaign provider specified. A scammer tag would be more appropriate, if necessary.
It's not against the forum rules to have any amount of accounts, though they can be banned for ban evading if you have been banned before. It's up to each signature deal to state whether a user can have more than one account on their deals, but that's going to be pretty hard to police unless it's obvious. Scammer tags aren't given out by this forum any more either.